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    <title>Document</title>
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    <p>中国</p>
    <p>武汉</p>
    <p class="jy">加油</p>
    <p id="wan">祖国万岁</p>
    <h3 class="jy">祖国万岁</h3>
    
    <script src="js/jquery-3.4.1.min.js"></script>
    <script>
        $("p").css("color","red"); // 标签选择器，获得所有的p
        $(".jy").css("color","red"); //类选择器
        $("#wan").css("color","red"); //ID选择器,更具备唯一性
        $(".jy,#wan").css("color","red"); // 并集选择器，.jy和#wan
        $("h3.jy").css("color","red"); // 交集选择器，既是h3标签，又拥有.jy的元素
    </script>
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